1. Field Of The Invention
This invention is in the field of fuel injection systems for internal combustion engines, and particularly fuel injection system for four stroke cycle engines which inject the fuel into the engine intake manifold.
2. Description Of The Prior Art
Within the past several years the gasoline engine carburetor has been largely replaced with intake manifold gasoline injector systems in many engine applications. Most of these prior art gasoline injector systems inject the fuel at constant pressure and control the fuel quantity by controlling the time duration of injection. An electronic controller, responsive to engine intake air flow rate and engine speed sensors, adjusts time duration of fuel injection so as to maintain the desired overall air to fuel ratio created in the intake manifold. The electronic controller can be additionally responsive to engine exhaust gas composition sensors which provide a feedback control to more closely adjust fuel injection duration, and hence overall air to fuel ratio, for minimum emission of undesirable exhaust gas constituents. This capability of using a feedback control from the exhaust is a principal reason why carburetor fuel systems were replaced with fuel injector systems, since it is difficult to properly introduce feedback control into a carburetor system.
A particular benefit of typical carburetor fuel systems is that the instantaneous rate of fuel flow is roughly proportional to the instantaneous rate of air flow. As a result, during each engine intake stroke, regions of excessively lean air to fuel ratio and other regions of excessively rich air to fuel ratio can be largely avoided and a roughly uniform instantaneous air to fuel ratio is created in each intake mixture charge going into each engine cylinder.
Present gasoline injector systems tend to create both excessively rich air fuel mixture regions and excessively lean air fuel mixture regions since the instantaneous rate of fuel flow is not proportioned to the instantaneous rate of air flow into the engine intake manifold. While fuel injection is taking place an over rich region is created, and, after injection ceases an over lean region is created during each engine intake stroke. The over rich region and the over lean region survive compression, in large part, and their subsequent combustion creates undesirable emission components characteristic of both over lean operation and over rich operation even though the overall air fuel ratio is neither over rich nor over lean.
A principal undesirable exhaust emission from over lean mixtures is oxides of nitrogen, whereas from over rich mixtures carbon monoxide and unburned hydrocarbons are among the undesirable exhaust emissions. Between these over lean mixtures and over rich mixtures a rather narrow "window" of mixture ratios exists where net emissions of both types of undesirable exhaust constituents can be minimized. Yet, even when the overall mixture ratio of an engine lies within this narrow "window," excess emissions may occur if this overall mixture is non uniform and stratified, as when present gasoline injector systems are used which create both over lean regions and over rich regions within each air fuel mixture charge going into each engine cylinder.
It would be very beneficial to have available a gasoline fuel injection system, capable of proportioning instantaneous fuel flow rate to instantaneous air flow rate so that a uniform mixture ratio existed, and lying within the minimum net emissions window, for each air fuel mixture charge going into each engine cylinder. Yet further reductions of undesirable exhaust emissions could be achieved in this way.